The invention relates to a differential for dolly, particularly for shootings in the TV and movie fields.
More specifically, the invention concerns a differential allowing to obtain by a single control all the configurations of the dolly""s wheels required during the shootings.
As it is known, dollies are trolleys used since many years in the field of the shootings, on which the shooting means and the cameraman are placed, pushed by the man in charge of the manoeuvring of the same dolly.
It is a very delicate and basic instrument for shootings, since an optimum control of the dolly allow to make high quality shootings. To this end, many improvements of the same dollies have been realised during the recent years, aiming to obtain the most reliable, soft and silent operation.
It is also known that said trolleys can work both along rails and directly on the floor and that, according to the needing it can be necessary to operate with different steering configurations or modes, namely two steering wheels, four steering wheels, and with the so called xe2x80x9ccrabxe2x80x9d configuration.
To obtain the different configurations of the wheels of the trolley, that is obviously provided with two front wheels and two rear wheels, it is necessary to provide different transmission means from the control bar on which the dolly operator acts.
At present, no solution exists allowing to directly and solely act on the control bar to indifferently obtain the above mentioned three configurations.
In fact, solutions presently available on the market provide on the control bar only the possibility of configuring the wheels according to the crab configuration and with two steering wheels, while to obtain the four steering wheels configuration different control and actuation means are provided in some solutions, or, in other cases it is even necessary to directly operate on the wheels of the dolly to obtain the required configuration.
It is evident that said solutions are not particularly advantageous for many reasons, particularly to be connected with practical considerations, deriving from the needing of interrupting the use of the dolly to obtain the different configurations, solution not accessible by the final user, structurally complex and expensive.
The above is due to the fact that none has been able until now to realize a technical solution allowing to have a differential suitable to obtain by the same control bar all the three required configurations.
In view of the above, the Applicant has studied and realized a technical solution for a differential able to solve all the above mentioned problems.
Particularly, main object of the present invention is that of providing a technical teaching for the realization of a differential allowing to obtain all three the configurations, respectively two and four steering wheels and crab, only acting on the control bar.
It is therefore specific object of the present invention, a differential for dolly, particularly for shootings in the TV and movie fields, comprising a first inlet axis, coupled with a selection and control bar, provided on the dolly, for the selection of one among the two steering wheels, four steering wheels or crab configuration, said inlet axis being provided with motion transmission means for the two steering wheel configuration, with motion transmission means for the four steering wheel configuration, and with motion transmission means for the crab configuration; a motion output axis; and two lateral axes, respectively for the transmission to the left wheel and to the right wheel, said inlet axis and said output axis providing central movable axis to selectively engage said transmission means, coupled at the bottom with rocking lever means, transmitting the position of the movable central axis of the inlet axis to the movable central axis of the output axis.
Preferably, according to the invention, said lateral axes provide motion transmission means to the relevant rear wheel and blocking means for the same wheels in case of two steering wheel configuration.
According to a first embodiment of the differential according to the invention, said two steering wheel and four steering wheel motion transmission means can provide elliptical gears, provided on said inlet, transmission and output axes, having a profile suitable to the kind of selected motion.
In a second embodiment of the differential according to the invention, said two steering wheel and four steering wheel motion transmission means can provide cam structures, preferably double cam structures, with a profile realised on said cam, shaped in function of the particular motion to be transmitted, slide guided by rolls, the motion of the transmission axis and/or output axis being transmitted by chains or direct transmission.
Always according to the invention, said inlet, transmission, output and right and left axes can be provided between an upper plate and a lower plate, holes being provided on said plates for the passage of said axes.
Furthermore, according to the invention, said axis can be coupled by motion transfer gears.